FIELD OF THE INVENTION
The present invention relates to an MPEG-2 system decoder for use in a video receiving apparatus. More particularly, the present invention relates to a method of reducing a channel hopping time in an MPEG-2 system decoder by minimizing the response time in the receiver when the 10 receiving channel is changed.
Generally, when a broadcasting signal is received using the MPEG-2 system decoder, program specific information (PSI) is used for reception. The PSI includes a program association table (PAT), program map table (PMT), network information table (NIT), conditional access table (CAT), etc. The PAT has a PMT packet identifier (PID) for all programs, and the PMT has video and audio PID information corresponding to each program. The NIT has information on physical network parameters such as FDM frequency and the number of transponders. The CAT has PID information for an entitlement management message (EMM) and so on. The PAT, PMT, and CAT are composed of 1024 bytes, i.e., 6 packets (1 packet=188 bytes) in maximum length, and the NIT is composed of 4096 bytes in maximum length.
FIG. 1 shows a conventional PID detecting structure in an MPEG-2 system decoder. Referring to FIG. 1, the conventional PID detecting structure is provided with a host processor 10, a PID register 11, a PID detecting section 12, a dynamic random access memory (DRAM) 14, and a DRAM interface 13. The PID detecting section 12 detects the PID from an input bit stream and provides the detected PID to the DRAM interface 13. The DRAM interface 13 transmits the PID output from the PID detecting section 12 to the DRAM 14. Concurrently, the DRAM interface transmits a PID read-out from the DRAM 14 to the host computer 10. The DRAM 14 stores the PID input through the DRAM interface 13, and provides a stored PID to the host computer 10 through the DRAM interface 13. The host computer 10 reads out the PMT PID values stored in the DRAM 14 and analyzes the read-out data to control the PID detecting section 12. A desired PID is output from the host to the detecting section through the PID register 11. The host computer 10 also performs search operations for the PID of the audio and video signals of a selected program by analyzing the PID read out from the DRAM.
The operation of the conventional MPEG-2 system decoder while searching for the audio and video PID of a selected program will now be explained in detail. When a PAT is input to the decoder, the PAT is stored in the DRAM 14. The host computer 10 reads out and analyzes the PAT stored in the DRAM 14 to determine the PMT PID of a selected program. The host computer 10 then outputs the corresponding PID value to the PID register 11, so that the PID detecting section 12 detects a packet having the corresponding PID value and stores the detected packet in the DRAM 14. If all the PMTs are stored in the DRAM 14, the host computer 10 reads out from the DRAM 14 and analyzes the corresponding information, determines the audio and video PID value corresponding to the selected program, and then performs detection of the audio and video signals in accordance with the PID value.
The conventional PID detecting system suffers from the disadvantages in that it requires a long channel hopping time because the audio and video PID corresponding to the selected channel can only be found after all the PSI packets are received after power up. Further, when the power is initially input or when channel selection is made, the conventional system requires sequential access to the PAT, PMT, etc. stored in the DRAM 14 and then analysis of the accessed data in order to find out the audio and video PID corresponding to the program of a selected channel. This results in a long response time.